44 preCISIon. We and the Russians reside on a planet-planets more likely being condensations of the nebular envelope noticeable on other stars than the debris of a brush the sun had with star x. Contrary to what is sometimes sup- posed, there is no reason to be ashamed of the sun. While not so big as Antares or so dense as Sirius B, It is a little above average in most respects. Neither blue giant nor red dwarf, it has its own secure nIche in the yellow band, and lies comfortably between vast extremes of stellar size, density, and absolute brigh tness. If An tares were placed In the sun's posItion, it would engulf the orbit of Mars, whereas van Maanen's star, smaller than Neptune, would warm us hardly at all. A cubic inch of Sirius B would weIgh three-fourths of a ton on the earth, whereas air at the earth's surface is a hundred times more sub- stantial than the mean density of Betel- geuse. Curiously (and without doubt significantly), the variability of stars in regard to mass is surprisingly restrict- ed; all are between one-tenth and fifty times the weight of the sun, whose tonnage is 1,980 followed by twenty- four zeros. The sun, with its family (a crew including the playful comets, whirling in and out of ken on elliptical orbits, and the darling asteroids, few bigger than Pennsylvania and some no bigger than a grand piano), is situated about halfway between the center of the galaxy-taken to he the brilliant star-clouds in Sagittarius-and the rim. Our galaxy, too, is something to be proud of. A flat spiral a hundred and twenty thousand light-years in diameter and about a tenth as thick, it contains ,1fI? e>t.. -=-.. , ) Þ J "Oven-ready costs a few cents more and oven-ready tS worth a few cents more!" NOVEMDER 2. , 1957 . not only the six thousand stars you can see on a clear night-which were most- ly named by Greeks before 500 B.C., w hen their heads were still ful1 of the Argonauticallegends-but from one to two hundred billion more. It also con- tains quantities of dust and gas and "dark matter." Luminous nebulae are excited to brightness by ultraviolet ra- diation from nearby stars, and nebulae with no stars at hand appear as shadows, in queer shapes-that of a horse's head, for instance, in Orion. Dark nebulae ac- count for the holes in the Milky \Vay- this celebrated path being the profusion we see when we look through our gal- axy the long way, toward the edge of the coin. In all galaxIes, the dark matter greatly outweighs the luminous. Beyond the void that surrounds our galaxy, the nearest neighbors are the two Magel- lanIc Clouds, gauzy bits visible in the Southern Hemisphere; these are a hun- dred and fifty thousand light-years away-hailing distance, as cosmic prox- imities go-and may be satellites of our galaxy. A true rival is the great spiral nebula In Andromeda, more than two million light-years distant. As we noted above, they are still counting other galaxies, but already the figure runs in to the millions, as does everything else in this realm. For instance, no matter how rare the circumstances that lead to the creation of planets habitable by in telli- gent lIfe, the probabilities suggest that there are millions of such planets in the universe. The trick is to reach them. Astronomical billions have become as familiar to us as the friendly face of our annua] budget. Yet when it comes to space travel, Man may get all dressed up and have no place to go. The other planets, stIll several technological mag- nitudes away, are, at the most optimistic conjecture, as congenial as a combina- tion of Antarctica and a sewer main, and beyond them the leap is great, de- spite all the plausible speculation about how slowly the wristwatch of a space traveller will tick as he approaches the speed of light. After our sun, the near- est star is a million times as distant as the nearest planet- V en us, which dares j venture to within twenty-four million miles of us. If the sun is the dot over this "i," the next-nearest star, Proxima Centauri, is ten miles away. Space is thInly populated; Jeans estimated that if all the matter known to exist were evenly distributed, the density of the universe would be 10- 30 that of water. ( 10- 1 is one-tenth, 10- 2 is one-hun- dredth, etc.) The velocities that even General LeMay can achieve will not unduly impress the universe. In addi- tion to accomplishing its own revolu-